Dave --
With the exception of this one, Chamaesyce inequilatera, all Chamaesyce names are now synonyms for Euphorbias. Can all the names be changed in the database at once to reflect that they are synonyms or does each have to be done individually, connecting them to the Euphorbias with which they are synonymous?

That doesn't seem feasible because it might not be just a genus change in some cases. I just clicked on one in ITIS, Chamaesyce petaloidea, and it's now a synonym of Euphorbia missurica. Are all of the ones currently in the database simple genus changes or will the species also change for some?

Good. That's the right solution. ITIS doesn't recognize C. inequilatera, by the way, and ITIS also says that the whole genus is now Euphorbia (as of 2011). Is it possible that The Plant List information (as of 1987) should be reversed? Maybe C. inequilatera is a synonym of Euphorbia sanguinea instead of the opposite.